This is a question that I'm sure many people have asked themselves. But not having a spare TPS to pull apart, most are destined to live out their lives without ever achieving black-belt level in TPS knowledge. Never fear... help is at hand

This is the throttlebody side of the TPS... what you see when you take it off.

This is the other side with the plastic cover removed.

The metal "wipers" that rotate with the throttle and run on the carbon tracks.

And the carbon tracks that complete the circuits and provide resistance.

This particular TPS (89452-12050) came from an AE82 if I remember correctly, but it is of the same era as the AW11 and AE86, so should be near enough the same. It is not designed to be opened so therefore should be considered non-repairable. The clips that hold the back cover on have to be broken to get the cover off. Under the cover is a thin rubber diaphragm/sealing gasket, and below that the white board for the carbon tracks. The board is gripped by clips that are part of the TPS output pins.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

Interesting, I have wondered what was in there. I also wonder what makes one different from another for various engines. Is it simply the bolt and throttle fitting? And when they go bad is it just wear of the wiper tracks? They seem to cost more than they should. Anyway thanks for getting us to black-belt TPS level.

Toyota often use the same component under different part numbers on several models. I see this particular TPS is also suited to certain Lexus cars as well as AW11 and Corollas. It is a key component in your car driving well, so it needs to be a quality item. And the dealership network has to keep inventory available for the expected lifetime of the vehicle (about 20 years IIRC), so they are gonna cost

But these days you can usually find a China made version on Ebay for cheap, or grab a second hand one from somewhere, so no need to pay dealership prices if you are on a budget.

While virtually all older TPS's have the same basic design, each car manufacturer will have variations in housing design, plug, orientation with the throttle spindle, resistance values etc. This helps to avoid installing the wrong TPS for the engine. A late model TPS will usually have three pins instead of four (no IDL switch).

Because the TPS spends most of its life at the low throttle openings, the tracks tend to wear out near the start of its sweep. They don't like water inside them either. But apart from that they are a pretty reliable item and should be good for 200k plus miles of normal driving.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

On my ae82 with the 4age, on and off low throttle is accompanied by a lurch, as best as I can describe it. It's either accelerating or closed throttle. I've adjusted the TPS by the service manual's resistance method, but I expect my adjustment is off a fraction. Any suggestions?

The transition of the engine from "idling" to "running" is controlled by the idle (IDL) switch on a 4-wire TPS. The switching point is when the wipers just come into contact with and bridge the two stubby tracks you can see in the above pics.

The switch should be closed when the throttle arm is on the stop or very close, and open once the arm moves away by a small distance. Operation of the switch can be confirmed by connecting your multimeter to the two appropriate pins on the TPS. You are setting the switching point when you use the two different feeler gauges between the throttle arm and the stop. The procedure is described in the factory service manual.

Generic image but you get the idea

While you have your multimeter out, you can also connect between the ground signal pins and check how the resistance value changes as you move the throttle arm. An analog meter makes this very easy as you are looking for a smooth change in value from closed to open without any sharp jumps or dropouts. If you find that there is a gap (dropout) right at the moment the throttle starts to come off the stop then you are looking for a replacement TPS.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.